Automatic thermal runaway isolation system of energy storage cabinet and control method of automatic thermal runaway isolation system

Abstract

The invention belongs to the technical field of distributed energy storage system safety protection and battery thermal management, and discloses an energy storage cabinet thermal runaway automatic isolation system which comprises a sensing module, an execution module, a supporting module, a constraint module, a damping module and an isolation module. Through physical isolation, reliability is high, no fire extinguishing medium is needed, pure mechanical action is achieved, meanwhile, a two-stage insurance mechanism is adopted, and the comprehensive success rate is high; the system is completely autonomous, unattended operation is feasible, BMS automatic detection, automatic decision making and automatic execution are achieved, the system does not depend on external fire control intervention, and the system is suitable for remote areas such as 5G base stations and photovoltaic power stations; the economical efficiency is prominent, no consumables are needed (fire extinguishing agents do not need to be filled regularly), and the cost can be effectively saved; the structure is simple, the integration degree is high, the lock body side installation does not occupy internal space, the horizontal spring bolt supports, stress distribution is uniform, and disassembly, assembly and maintenance are easy and convenient. And the method has wide adaptability, is compatible with various battery pack specifications and supports various battery chemical systems.

Description

Technical Field

[0001] This invention belongs to the field of distributed energy storage system safety protection and battery thermal management technology, specifically an automatic isolation system for thermal runaway of energy storage cabinets and its control method. Background Technology

[0002] Against the backdrop of the rapid development of the energy storage industry, thermal runaway accidents occur frequently. In recent years, the number of domestic energy storage fire accidents has increased by more than 300%, with the cost of a single fire extinguishing ranging from 500,000 to 800,000 yuan and maintenance costing more than 580,000 yuan over 10 years. In remote areas (5G base stations, photovoltaic power stations), there is no one on duty, and traditional fire extinguishing solutions are ineffective. Existing solutions (fire extinguishing agents, gas flooding, fine water mist) have a success rate of 85%-95%, but there is still a 15% risk.

[0003] The existing prevention and control solutions have the following shortcomings: Fire extinguishing solutions: rely on consumables (agents / gases need to be refilled regularly), fire intervention is delayed, unattended scenarios are not feasible, the fire extinguishing success rate is 85%-95%, there is still a risk of failure, and the cost is high; Passive pressure relief solutions: pressure relief is difficult to control precisely, gas leakage pollutes the environment, combustion heat is dissipated outwards, and isolation is not possible; Cooling and heat dissipation solutions: freezing failure occurs in extremely low temperature environments, thermal runaway temperature rise rate is in seconds, and heat dissipation response is delayed, therefore, improvements are needed. Summary of the Invention

[0004] The purpose of this invention is to provide an automatic isolation system for thermal runaway of energy storage cabinets and its control method, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: an automatic thermal runaway isolation system for energy storage cabinets, comprising: a sensing module, an execution module, a support module, a constraint module, a damping module, and an isolation module. The sensing module consists of a temperature sensor and a BMS control system. The execution module consists of four sets of sidewall electromagnetic lock units, each of which includes an electromagnetic coil and a pulling mechanism. The support module consists of a horizontally supporting locking tongue; The constraint module consists of a dual-rail guide unit, used to constrain the vertical downward movement of the locking tongue; The damping module consists of a gas-liquid buffer damping cylinder; The isolation module consists of an underground isolation pit.

[0006] As a preferred embodiment of the present invention, the side wall electromagnetic lock unit is installed on the left and right side walls of the cabinet, with two units on each side in a symmetrical arrangement, 300-400mm from the ground. The specifications of the electromagnetic coil of the side wall electromagnetic lock unit are as follows: operating voltage DC 24V; single suction force 500N; response time <100ms; operating temperature -40~+70℃; protection level IP67. The materials selected for the horizontal support latch are as follows: the main body is 316L stainless steel (φ25mm×100mm); the constraint component is a Bi-Sn eutectic alloy constraint component (16mm diameter spherical); the heat insulation coating is a ceramic-based coating (2mm thick); the dimensions of the horizontal support latch are: extension length 150-180mm; diameter φ25mm; load-bearing cross-sectional area 491mm². 2 Actual stress 2.9 MPa (safety factor > 50).

[0007] As a preferred embodiment of the present invention, the Bi-Sn eutectic alloy constraint has a Bi:Sn ratio of 58:42; a working temperature threshold of 700±10℃; and melting characteristics of room temperature strength >1.5MPa (firm constraint), 700℃ strength ≈0 (completely liquid), and melting time <1 second.

[0008] As a preferred embodiment of the present invention, the dual-rail guiding unit is configured with one φ16mm guide rail installed on each of the left and right sides; length ≥1500mm (covering the entire descent path); accuracy ≥h7 level; The number of gas-liquid buffer damping cylinders is four (one at each of the four corners), and they adopt adjustable throttling orifices, with an adjustable descent speed range of 0.1-0.5m / s; the parameters of the gas-liquid buffer damping cylinders are: stroke 150-200mm; working pressure 10-20bar (adjustable); response reliability 99.9%+; working life >1 million cycles.

[0009] As a preferred embodiment of the present invention, the depth of the underground isolation pit is 0.4-0.5m; the size is >1200mm×600mm (allowing for the shape of the battery pack); the bottom structure is as follows: fireproof sand / clay paving (20cm thick); heat insulation board (to reduce heat conduction); vent hole (to prevent overpressure).

[0010] As a preferred embodiment of the present invention, the system also integrates a BMS self-diagnostic function for periodically testing key components such as electromagnetic coils and sensors.

[0011] To achieve the aforementioned other objective, the present invention also provides the following technical solution: a control method for automatic isolation of thermal runaway in an energy storage cabinet, the specific steps of which are as follows: Step 1: The BMS monitors the cell temperature in real time and makes judgments based on multiple parameters; Step 2: When T≥120℃ is detected, the first level of electromagnetic isolation is triggered; Step 3: The controller sends a 24V pulse to the four electromagnetic coils, generating a total tensile force of 2000N; Step 4: Pull the lever to release the unlocking pin, releasing the Bi-Sn eutectic alloy constraint, and the locking tongue will retract quickly (<200ms). Step 5: The gas-liquid buffer damping cylinder is activated synchronously to precisely control the descent speed of the battery pack; Step 6: The battery pack falls vertically under the constraint of the guide rail and enters the isolation pit (<10 seconds). Step 7: If the first-level isolation fails (T≥700℃), the second-level heat-fusion isolation will be automatically activated.

[0012] As a preferred embodiment of the present invention, the specific process of the first-level electromagnetic isolation is as follows: Triggering conditions: BMS detects cell temperature ≥120℃; Level 3 algorithm confirms loss of control (multiple parameters simultaneously abnormal); Controller sends 24V pulse signal; Four electromagnetic coils are simultaneously energized (unit: 500N × 4 = 2000N total pulling force); Pull rod pulls unlocking pin, releasing Bi-Sn eutectic alloy constraint; Lock tongue quickly retracts to side wall (time <200ms); Gas-liquid buffer damping cylinder starts synchronously, precisely controlling the descent speed (0.2-0.3m / s); Battery pack falls smoothly and vertically under guide rail constraint; Battery pack completely enters isolation pit (time <10 seconds); Isolation complete.

[0013] As a preferred embodiment of the present invention, the specific process of the second-stage hot melt isolation is as follows: Extreme failure conditions: main power failure, simultaneous failure of all four electromagnetic coils (probability <0.01%), all four locking tongues jammed; temperature continues to rise to 700℃; Bi-Sn eutectic alloy restraints melt rapidly (losing all restraint capabilities within <1 second); pull rod completely disengages from restraint; electromagnetic lock remains stationary, battery pack detaches under its own weight; gravity pulls the battery pack down into the isolation pit; isolation complete.

[0014] The beneficial effects of this invention are as follows: This invention features high reliability through physical isolation. The battery pack itself is a heat source, and removal immediately isolates it without the need for any fire extinguishing agents. It operates purely mechanically and incorporates a two-level safety mechanism, resulting in a high overall success rate. It is fully autonomous and feasible for unattended operation. The BMS automatically detects, makes decisions, and executes actions without relying on external fire intervention, making it suitable for remote areas such as 5G base stations and photovoltaic power plants. It is highly economical, requiring no consumables (no need for periodic refilling of fire extinguishing agents), effectively saving costs. It has a simple structure and high integration. The side-mounted lock body does not occupy internal space, and the horizontal locking tongue provides uniform stress distribution, making disassembly and maintenance simple. It has wide adaptability, compatible with various battery pack specifications (4U-12U) and supporting multiple battery chemistry systems (LFP / ternary / sodium ion, etc.). It can be integrated into existing energy storage systems without significant modifications. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the lock body installation of the present invention; Figure 2 This is a side view of the lock body of the present invention; Figure 3 This is a structural diagram of the battery pack isolation tunnel of the present invention; Figure 4 This is the parameter table for the electromagnetic lock of the present invention; Figure 5 This is a table of horizontal support latch parameters for the present invention; Figure 6 This is a parameter table for the Bi-Sn eutectic alloy constraint component of the present invention; Figure 7 This is a parameter table for the gas-liquid buffer damping cylinder of the present invention; Figure 8 This is a table of overall performance parameters for the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] like Figures 1 to 8 As shown, this embodiment of the invention provides an automatic thermal runaway isolation system for energy storage cabinets, including: a sensing module, an execution module, a support module, a constraint module, a damping module, and an isolation module. The sensing module consists of a temperature sensor and a BMS control system; The execution module consists of four sets of sidewall electromagnetic lock units, each of which includes an electromagnetic coil and a pulling mechanism; The support module consists of a horizontally supporting locking tongue; The constraint module consists of a dual-rail guide unit, used to constrain the vertical downward movement of the locking tongue; The damping module consists of a gas-liquid buffer damping cylinder; The isolation module consists of an underground isolation pit.

[0018] Example 1: Application of Photovoltaic Energy Storage Power Station Project scale: 100kWh LFP battery energy storage cabinet Battery pack specifications: Dimensions: L1200mm×W600mm×H400mm; Weight: 580kg; Number of packs: 4 battery packs (25kWh×4); Isolation system configuration: Electromagnetic locks: 4 sets × 1200 yuan = 4800 yuan; Lock tongue: 316L stainless steel = 3200 yuan; Bi-Sn restraint parts: ×4 = 1600 yuan; Guide rail system: φ16×2×2m = 2400 yuan; Hydraulic buffer cylinders: 4 units = 8000 yuan; Isolation pit construction: concrete + fireproof materials = 24000 yuan; Control circuit: BMS integrated module = 6000 yuan; Total investment: 50000 yuan (approximately 75% saving compared to fire extinguishing solutions); Working process: Normal operation: 4 latches extend to support the battery pack; Thermal runaway (T≥120℃): Electromagnetic lock activates, latches retract; Battery pack falls smoothly (<10 seconds) and enters the isolation pit; Completely isolated from the outside world, heat is safely dissipated; Example 2: Backup Power Supply for 5G Base Stations Application scenario: 5G base stations in remote mountainous areas (unattended) Battery pack specifications: 6U rack-mounted; 48kWh LFP battery module weight: 400kg; Key advantages: Completely self-isolated, not reliant on external fire protection; low initial investment, no maintenance costs for 10 years; reliable operation in extreme environments (high cold / high temperature); meets the "zero-failure" construction requirements for 5G base stations; Example 3: Battery Swapping Station for New Energy Vehicles Application scenario: Battery swapping stations in highway service areas Battery pack specifications: 8U standard battery swapping pack; 75kWh battery capacity; weight: 650kg; Core requirements: Rapidly isolate faulty batteries and restore operations; prevent thermal runaway from affecting surrounding battery swapping stations; high degree of automation and low operating costs; System configuration: 4 sets of electromagnetic lock units; dedicated guide rails and buffer mechanisms; integrated BMS control; fully automatic isolation process.

[0019] The side wall electromagnetic lock units are installed on the left and right side walls of the cabinet, with two units on each side in a symmetrical arrangement, 300-400mm from the ground. The specifications of the electromagnetic coils of the side wall electromagnetic lock units are as follows: operating voltage DC 24V; single suction force 500N; response time <100ms; operating temperature -40~+70℃; protection level IP67. The materials selected for the horizontal support latch are as follows: the main body is 316L stainless steel (φ25mm×100mm); the constraint component is a Bi-Sn eutectic alloy constraint component (16mm diameter spherical); the heat insulation coating is a ceramic-based coating (2mm thick); the dimensions of the horizontal support latch are: extension length 150-180mm; diameter φ25mm; load-bearing cross-sectional area 491mm². 2 Actual stress 2.9 MPa (safety factor > 50).

[0020] Under normal conditions, the electromagnetic lock unit on the side wall is de-energized, the lever remains stationary, and the bolt remains extended. Under thermal runaway conditions, the BMS detects a temperature T>120℃ and energizes the coil. When the bolt retracts, the magnetic force pulls the lever, and the bolt quickly retracts to the side wall, releasing the constraint. The horizontal support bolt design features: the bolt extends horizontally, directly supporting the four corners of the battery pack bottom surface; the load-bearing capacity of a single bolt is >1450N (corresponding to 1 / 4 of the weight of a 580kg battery pack + a safety factor); when the guide is disengaged, the bolt retracts synchronously in the double guide rails to prevent tilting.

[0021] Among them, the Bi:Sn ratio of the Bi-Sn eutectic alloy constraint component is 58:42; the working temperature threshold is 700±10℃; the melting characteristics are: room temperature strength >1.5MPa (firm constraint), 700℃ strength ≈0 (completely liquid), and melting time <1 second.

[0022] When the Bi-Sn eutectic alloy constraint is operating normally (<100℃): the Bi-Sn constraint is intact and the pull rod cannot move; in the early stage of thermal runaway (120℃): the electromagnetic lock is activated and the pull rod is pulled to release the constraint; in extreme cases (700℃+): even if the electromagnetic lock fails, the Bi-Sn melts and the lock tongue automatically disengages; the isolation success rate is ensured to be >99.99% through double insurance.

[0023] The dual-rail guiding unit is configured with one φ16mm guide rail installed on each of the left and right sides; the length is ≥1500mm (covering the entire descent path); and the accuracy is ≥h7 level. The gas-liquid buffer damping cylinder consists of four cylinders (one at each of the four corners), with adjustable throttle orifices, and the descent speed is adjustable from 0.1 to 0.5 m / s. The parameters of the gas-liquid buffer damping cylinder are: stroke 150-200 mm; working pressure 10-20 bar (adjustable); response reliability 99.9%+; working life > 1 million cycles.

[0024] The dual-rail guiding unit is used to constrain the locking tongue to sink vertically, preventing the battery pack from tilting or shifting laterally, and precisely controlling the disengagement trajectory; the working principle of the gas-hydraulic buffer damping cylinder is as follows: when the locking tongue retracts, the hydraulic cylinder starts synchronously; the flow of oil is precisely controlled through the throttle orifice; the battery pack's falling speed is constrained within the range of 0.2-0.3m / s.

[0025] The underground isolation pit is 0.4-0.5m deep and >1200mm×600mm in size (with allowance for the shape of the battery pack). The bottom structure is as follows: fireproof sand / clay lining (20cm thick); heat insulation board (to reduce heat conduction); vent holes (to prevent overpressure).

[0026] The underground isolation pit physically isolates the heat source from the outside world, allowing the combustion heat to dissipate downwards into the isolation pit, thus preventing the flames from spreading to other battery packs.

[0027] The system also integrates BMS self-diagnostic function for periodic testing of key components such as electromagnetic coils and sensors.

[0028] The BMS self-diagnostic function uses advanced sensors and sophisticated algorithms to monitor various battery parameters in real time. If these parameters become abnormal, the BMS system will react quickly, such as issuing an alarm or cutting off the charging or discharging circuit, to prevent the battery from being damaged due to overcharging, over-discharging, or overheating, thereby extending the battery's lifespan.

[0029] This invention also provides a control method for automatic isolation of thermal runaway in energy storage cabinets, the specific steps of which are as follows: Step 1: The BMS monitors the cell temperature in real time and makes judgments based on multiple parameters; Step 2: When T≥120℃ is detected, the first level of electromagnetic isolation is triggered; Step 3: The controller sends a 24V pulse to the four electromagnetic coils, generating a total tensile force of 2000N; Step 4: Pull the lever to release the unlocking pin, releasing the Bi-Sn eutectic alloy constraint, and the locking tongue will retract quickly (<200ms). Step 5: The gas-liquid buffer damping cylinder is activated synchronously to precisely control the descent speed of the battery pack; Step 6: The battery pack falls vertically under the constraint of the guide rail and enters the isolation pit (<10 seconds). Step 7: If the first-level isolation fails (T≥700℃), the second-level heat-fusion isolation will be automatically activated.

[0030] When the BMS monitors the cell temperature in real time, its control circuit includes a three-level runaway confirmation algorithm to reduce the probability of false triggering.

[0031] The specific process for the first level of electromagnetic isolation is as follows: Triggering conditions: BMS detects cell temperature ≥120℃; Level 3 algorithm confirms loss of control (multiple parameters simultaneously abnormal); Controller sends 24V pulse signal; Four electromagnetic coils are simultaneously energized (unit: 500N × 4 = 2000N total pulling force); Pull rod pulls unlocking pin, releasing Bi-Sn eutectic alloy constraint; Lock tongue quickly retracts to side wall (time <200ms); Gas-liquid buffer damping cylinder starts synchronously, precisely controlling the descent speed (0.2-0.3m / s); Battery pack falls smoothly and vertically under guide rail constraint; Battery pack completely enters isolation pit (time <10 seconds); Isolation complete.

[0032] The reason for choosing 120℃ as the threshold is that the cell temperature is <80℃ during normal charging and discharging, and <100℃ during fast charging (BMS limit). When an internal short circuit begins, the cell temperature rises rapidly to >120℃, clearly indicating a runaway signal. Choosing 120℃ as the threshold can avoid false triggering and ensure accurate judgment.

[0033] The specific process for the second-level heat-sealing barrier is as follows: Extreme failure conditions: main power failure, simultaneous failure of all four electromagnetic coils (probability <0.01%), all four locking tongues jammed; temperature continues to rise to 700℃; Bi-Sn eutectic alloy restraints melt rapidly (losing all restraint capabilities within <1 second); pull rod completely disengages from restraint; electromagnetic lock remains stationary, battery pack detaches under its own weight; gravity pulls the battery pack down into the isolation pit; isolation complete.

[0034] The peak combustion temperature of LFP batteries is 600-800℃. At 700℃, all metal restraints completely melt, and the Bi-Sn alloy completely liquefies and fails at this temperature. Therefore, choosing 700℃ can ensure that even if all active mechanisms fail, passive protection can still work.

[0035] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An automatic thermal runaway isolation system for an energy storage cabinet, characterized in that, It includes: a perception module, an execution module, a support module, a constraint module, a damping module, and an isolation module. The sensing module consists of a temperature sensor and a BMS control system. The execution module consists of four sets of sidewall electromagnetic lock units, each of which includes an electromagnetic coil and a pulling mechanism. The support module consists of a horizontally supporting locking tongue; The constraint module consists of a dual-rail guide unit, used to constrain the vertical downward movement of the locking tongue; The damping module consists of a gas-liquid buffer damping cylinder; The isolation module consists of an underground isolation pit.

2. The automatic thermal runaway isolation system for energy storage cabinets according to claim 1, characterized in that: The side wall electromagnetic lock units are installed on the left and right side walls of the cabinet, with two units on each side in a symmetrical arrangement, 300-400mm from the ground. The specifications of the electromagnetic coil of the side wall electromagnetic lock unit are as follows: operating voltage DC 24V; single suction force 500N; response time <100ms; operating temperature -40~+70℃; protection level IP67. The materials selected for the horizontal support latch are as follows: the main body is 316L stainless steel (φ25mm×100mm); the constraint component is a Bi-Sn eutectic alloy constraint component (16mm diameter spherical); the heat insulation coating is a ceramic-based coating (2mm thick); the dimensions of the horizontal support latch are: extension length 150-180mm; diameter φ25mm; load-bearing cross-sectional area 491mm². 2 Actual stress 2.9 MPa (safety factor > 50).

3. The automatic thermal runaway isolation system for energy storage cabinets according to claim 2, characterized in that: The Bi-Sn eutectic alloy constraint has a Bi:Sn ratio of 58:42; a working temperature threshold of 700±10℃; and melting characteristics of room temperature strength >1.5MPa (firm constraint), 700℃ strength ≈0 (completely liquid), and melting time <1 second.

4. The automatic thermal runaway isolation system for energy storage cabinets according to claim 1, characterized in that: The dual-rail guiding unit is configured with one φ16mm guide rail installed on each of the left and right sides; length ≥1500mm (covering the entire descent path); accuracy ≥h7 level; The number of gas-liquid buffer damping cylinders is four (one at each of the four corners), and they adopt adjustable throttling orifices, with an adjustable descent speed range of 0.1-0.5m / s; the parameters of the gas-liquid buffer damping cylinders are: stroke 150-200mm; working pressure 10-20bar (adjustable); response reliability 99.9%+; working life >1 million cycles.

5. The automatic thermal runaway isolation system for energy storage cabinets according to claim 1, characterized in that: The depth of the underground isolation pit is 0.4-0.5m; the size is >1200mm×600mm (allowing for the shape of the battery pack); the bottom structure is as follows: fireproof sand / clay lining (20cm thick); heat insulation board (to reduce heat conduction); vent hole (to prevent overpressure).

6. The automatic thermal runaway isolation system for energy storage cabinets according to claim 1, characterized in that: The system also integrates BMS self-diagnostic function for periodically testing key components such as electromagnetic coils and sensors.

7. A control method for automatic isolation of thermal runaway in an energy storage cabinet, characterized in that, The specific steps are as follows: Step 1: The BMS monitors the cell temperature in real time and makes judgments based on multiple parameters; Step 2: When T≥120℃ is detected, the first level of electromagnetic isolation is triggered; Step 3: The controller sends a 24V pulse to the four electromagnetic coils, generating a total tensile force of 2000N; Step 4: Pull the lever to release the unlocking pin, releasing the Bi-Sn eutectic alloy constraint, and the locking tongue will retract quickly (<200ms). Step 5: The gas-liquid buffer damping cylinder is activated synchronously to precisely control the descent speed of the battery pack; Step 6: The battery pack falls vertically under the constraint of the guide rail and enters the isolation pit (<10 seconds). Step 7: If the first-level isolation fails (T≥700℃), the second-level heat-fusion isolation will be automatically activated.

8. The control method for automatic isolation of thermal runaway in an energy storage cabinet according to claim 7, characterized in that: The specific process for the first-level electromagnetic isolation is as follows: Triggering conditions: BMS detects cell temperature ≥120℃; Level 3 algorithm confirms loss of control (multiple parameters simultaneously abnormal); Controller sends 24V pulse signal; Four electromagnetic coils are simultaneously energized (unit: 500N × 4 = 2000N total pulling force); Pull rod pulls unlocking pin, releasing Bi-Sn eutectic alloy constraint; Lock tongue quickly retracts to side wall (time <200ms); Gas-liquid buffer damping cylinder starts synchronously, precisely controlling the descent speed (0.2-0.3m / s); Battery pack falls smoothly and vertically under guide rail constraint; Battery pack completely enters isolation pit (time <10 seconds); Isolation complete.

9. The control method for automatic isolation of thermal runaway in an energy storage cabinet according to claim 7, characterized in that: The specific process for the second-level heat-sealing insulation is as follows: Extreme failure conditions: main power failure, simultaneous failure of all four electromagnetic coils (probability <0.01%), all four locking tongues jammed; temperature continues to rise to 700℃; Bi-Sn eutectic alloy restraints melt rapidly (losing all restraint capabilities within <1 second); pull rod completely disengages from restraint; electromagnetic lock remains stationary, battery pack detaches under its own weight; gravity pulls the battery pack down into the isolation pit; isolation complete.

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